What the hell do these moisture meter readings actually mean? or, Have I got rising damp or not?

Electrical Moisture meters for damp diagnosis – oh yes.

A thing that raises an eyebrow amongst some independent surveyors is the way we so called ‘specialists’ seem happy to diagnose rising damp, or damp of any kind, using nothing more than our eyes and a conductivity moisture meter.

“Ha; I can get a reading off my fingertips or my head; I must have rising damp” scoff some.

It’s true; these meters give only a qualitative measurement. The figure is accurate, only in it’s relativity, to the previous reading – or the next. It will tell you if your head is dryer than your hand; even by how much; proportionately.

These meters cannot provide a true moisture content in masonry, plaster or indeed anything but wood; which many of them are calibrated for (and even then it’s only an approximation).

I know I’ve blogged on this before and you know all this already. But Graham Coleman has kindly sent me the table he drew up a long time ago and which all CSRT and many CRDS qualified surveyors will be all too familiar with, (though there’s always room for a quick refresher, hey lads)?

It’s the sad case that when I follow other surveyors on properties, where these meters have been used and where sometimes, diagnosis has been given; I often spot a problem. It’s the position of those little pairs of holes, which the meter pins leave behind; on the wallpaper and the paint. The thing is; they are almost invariably, just above the skirting board, maybe pearceing the plaster, an inch or two up and perhaps spaced a metre apart or more. They are rarely anywhere else.

What could these readings possibly tell the meter user?

Not much, I’m afraid. Maybe they were all very low? Well I suppose that’s something. Or maybe very high? Well there’s damp of some sort isn’t there? Oh dear; I fear they didn’t actually provide anything really usefull, from a damp diagnosis point of view. What a waste.

Look at Graham’s table; it’s the damp specialist’s version of Mendeleev’s periodic table; there may be gaps and things to add, but I think it’s a simple work of genius.

Graham Coleman's Moisture meter profiles

I know that reciting the periodic table doesn’t make you a chemist. In the same way, printing this and sticking it under the lid of your survey tool-box will not make a specialist of you. But is there a decent chemist who never checks the periodic table, just to check he’s on the right lines?

So, when surprised by that sudden, ardent bleeping from your meter, what to do? Take a look at the readings and then work away – up and left and right and maybe the skirting, (not relative), and repeat. Think and look at the table. You’ve already looked outside and all around the area, so do that again. Then when you’ve finished, you will almost certanly have a very accurate diagnosis.

My thanks go to Graham for the table and his tireless work in drumming all this stuff into my thick head over the past few years. Please remember that this is Graham’s work, not mine. If you want to copy it for your workbook, toolbox or thesis do so, but make sure Graham’s name stays on it please.

If you would like to use it commercially – ask Graham first; it’s his.

Dry Rot.

Oh, I forgot – nothing is ever written in stone; this is Graham’s take on his table…….

“These are some possible interpretations of moisture meter readings recorded at low level from walls; all have been validated by sampling and subsequent testing. There may be other interpretations of the same patterns but these are likely to be the most commonly encountered. There may also be other patterns but these are likely to be less common; for example, low level surface condensation might give a pattern similar to pattern ‘A’ but it will be purely a surface effect and highly likely to be obtained only during the colder months of the year. The important feature when using an electrical moisture meter is to record both vertical and horizontal patterns – one needs to interpret the pattern, not the actual figure. Remember, the patterns given are ‘possible’ interpretations.” Oh yes, pattern ’F’ – the damp-proofers nightmare – no work!

I agree to an extent. – Damp diagnosis is a specialist job and requires anyone doing it to consider all potential factors, which could give the profile. However, as a damp specialist I am expected to give my client a diagnosis, based on my survey. Most of the time I’m happy to give one and I rarely need to add any caviats like – possible – may be – could be or possibly.. Customers don’t like wishy washy reports so I try to avoid this.

There are times though, when one is stumped or the evidence does indeed point to something ‘not quite right’ – in these cases I agree that further investigation is needed. It’s not always straightforward.

I like overview patterns as they help you form a framework for investigating many things. Grahams work is very useful tool. I will put it in my brief case. I believe it is important not to mix fact with opinion and sometimes on initial inspections it is not possible to undertake tests to categorically define a cause as a matter of fact so possibilities have to be used to explain risk. It may be that further tests are recommended and the balance of the do nothing option explored. I assume “Dry rot” does casework which involves destructive testing until a result is certain and so he is right that all his comments can be expressed as factual. Surveyors must be careful not to sound authoritative by stating opinion as fact.This is where the word possible is useful. The client can expect your skill to assess a scale of risk in such cases so some measure should be found so as not to render comments valueless.

Nice to hear from you. I’m a big fan of Graham’s profile table and I’m glad you like it too, so simple and very intuitive.

I’m wary of getting too hung-up on semantics, where opinion and facts in reports come in; the spectre of the court room has a lot to answer for. I see too many survey reports which are so full of caveats and hedged bets, that their value to clients is dubious, to say the least. These reports are often the most expensive and lengthy ones too.

Giving my clients good information is the goal, but they shouldn’t be expected to understand all the technical issues (though some are fascinated by it and I like to indulge them when they are). Perhaps they may not have the time or inclination to want to ponder these things? In receiving my report, the last thing most need is a list of ‘maybe this’ and ‘maybe that’s’.

The diagnosis ought to be direct and specific; this can be given, without destructive or invasive testing – most of the time…………… in my opinion.

I’ve talked about this with Graham and others, who confirm that in over 95% of cases, a damp diagnosis, which is made using a moisture meter, common sense, experience, profiling and some methodology is correct, when checked later, using destructive lab methods.

Should we hedge our bets in a report and burden clients with risk analysis, and the pros and cons of this and that, for less than one twentieth occasions, when profiling may be wrong?

Of course, the above ratio assumes that all users of electrical moisture meters know how to use them, which is the rub and the reason I support the damp diagnosis group’s aims. I bet that the 1:20 ratio can be improved on and maybe reduce to nearer 1:100 if we all work together. I wouldn’t expect such a low success rate with my own meter or the majority of surveyors like yourself and other damp diagnosis group members, who are enthusiastic and serious about their work.

The numbers are relative only. They can be described as ‘per cent’ when the meter is being used in wood, because most meters are calibrated for average softwood. In masonry the same scale is used but if % is mentioned it is termed % WME – that is wood moisture equivalent. So that we if you see WME you know what the meter was reading – you don’t knoe how much water was there. In damp diagnosis it is often the relative distribution of moisture which tells a surveyor the most, rather than the exact moisture content.

In fact the exact moisture content is rarely important; 3% may be excessive in one type of plaster/brick and be acceptable in others…
Thank you for looking in, I hope the article helped you.

Hi im really disappointed i bought a stanley damp meter at B & Q for over £ 40 pounds yesterday i explained the problem to the chap serving me. He assured that information was inside the packaging on how to understand and interpret the readings. Got it home applied it and got severals readings which i cannot make head nor tail of flipping eck how maddening is that? From trolling on the web it appears to be a large problem and not just down to us blonde women (sorry blondes)! Could some one please just tell me if the readings are around 0.6 on the wood percent side , is this a problem or not ? If the outside brickwork after a dry period is reading around 20% is this a problem? (its above damp proofing). Many thanks if someone can help me make sense of this.
Caroline

I am really sorry I have taken so long to get back to you Caroline (spam bot problems),

I’m afraid that the readings taken outside should be forgotten about – they will fluctuate by the day and cannot be relied on. Remember the the damp meter readings are only accurate in timber – so 20% in wood is actually (about), 20%. Anything much above that in timber will cause rot unless the timber is protected by preservative.

When used in plaster – masonry or brick the readings are only qualitative – not quantitative. Indoors as a guide (though this is for a Protimeter MMS), not a B&Q DIY unit, I tend to ignore anything under about 24 in old houses… these meters are very sensitive and will pick up moisture that is just not a problem.

I never recommend DIY use as it takes years to really get to grips with these things in buildings.

If there’s no damp staining, salting, peeling or any other sign of damage then I’d say don’t worry about it. If you still are though, get advice via the PCA web site, to find a local contractor – independent surveyor or consultant.

I’m confused. Caroline’s question gave a figure of 0.6 but the reply was about percentages. Does this mean she has 60% moisture? That can’t be right. Our contractor got a reading of 0.9 on plaster and said it shouldn’t be more than 0.4? How does this tie in with percentages?
Thanks

Unfortunately I don’t know the moisture meter you are using so cannot tell what the readings are calibrated in. However, be very careful with anyone stating what is high and low on a meter on plaster. These meters can throw up very widespread levels and really, only an experienced surveyor should be using one. Also, one-off readings are not particularly useful. A moisture profile obtained by taking lots of readings across the area is the only useful way of using these meters on plaster or masonry. This doesn’t apply to readings from wood, where the readings can be taken as quantitative (as long as the levels are not very low or very high (over 35%), in which case just say they are very low or very high.

I have just recently bought a brand new built home. After living in my new home for a week I could smell damp coming from my kitchen walls behind the units. At week two I had a visit from our customer care manager who informed me that this would happen in some new builds and it was nothing to worry about that he would have someone come round and clean the walls. Four weeks later the smell was getting worse we finally had someone visit from the kitchen supplier to look at our damaged doors not the mould. After showing him the damaged doors I then showed him the mould that was now coming through the backing plates. He was disgusted that my kitchen was fitted with mould that bad being on the walls that it had now penetrated the backing plates. I waited a further three weeks for someone to come visit me to take backing plates off to see the damage behind the plates and on the walls, to our disgust it was all around three walls and black in most places. I had the customer care manager out the following week as no one else could attend when he was on holiday!! he again stated that this was a drying out process that this was normal and he would have someone come round clean this with water then bleach. I also had him check the walls with a moisture meter reader, the readings he got ranged from 20 at cupboard height to between 40 to 60 at skirting level height. This him informing me that this was due to the drying out process once again and this is normal readings. I informed him that I would be going on holiday the following day and I would prefer it if we could leave any countermeasures until I arrived back, this seeing if the levels have reduced as I left all cupboards open. I am returning on the 25th August, if the levels of moisture have not dropped and is still above 40, have you any ideas how I go about this issue as they informed me that they will be painting over the mould area that they cleaned with water and bleach ( this still black )and putting all cupboards back in although I think these are now damaged and should all be replaced. Your reply would be greatly appreciated

Ther is no way that you should be seeing mould inthis way. I would demand a new kitchen if it were me. Ther really should not be so much water that the amount of evaporation causes this. If the walls were wet plastered and then a kitchen installd the next day, well, that could do it. However, this is still a defect and the builder should rectify it IMHO. Any reading over 20% in internal joinery of any kind is way too high. You should be looking at between 8% and 14% max.

I own a ground floor flat which I rent out. After the last tenants moved out I could smell a lot of damp. The carpets were pulled up and I found damp on the back. The floors are concrete. Outside the living room window is a drain that was totally blocked by shrub roots. The council came and jet sprayed from the man hole and then put a camera down. After 16 meters (which is about a meter away from my flat) they found solid roots. I have been using a Digital Hygrometer in the bedroom and lounge. At the moment the readings in the lliving room are 68 over 25. I have being using a domestic dehumidifier in the living room for about 5 weeks which I am still emptying twice a day. The bedroom readings are around 74 over 22. There is no dehumidifier in the bedroom. I feel that this has been caused by the blocked drain. The report from the damp inspector says:
– Moisture meter testing showed readings in excess of 40% WME (wood moisture equivalent) to the porous plaster on walls.
-As readings exceed 20% WME remedial works are deemed necessary to this area.
and
The following defects were apparent and should be rectified by the council:
– Defective rainwater goods
– High plinth absorbing moisture from blocked gully.

As the council are the freeholders things are not moving very fast.. Can you tell me if the readings on the hygrometer are considered reliable. Someone told me that a comfortable reading would be between 45 and 50. Obviosly with the readings I have I am very concerned.
What do you think the remedial works will entail? I feel that to get the place dried out I should hire some industrial dehumidifires but am wondering if this is wise, should I wait for the council to do the work first?

The first thing is to fix the external defects. Then please read the following post If the flat is not occupied now I would make sure the heating is on (low) and the extract fans left running to dry the house. The hygropmeter readings are meaningless without lots of details such as occupancy, external vapour pressures and temperatures. Relative humity in homes should be kept below 60% if possible. However, be carefull, a perfectly dry house can have an RH of 75% plus, if it is cold (RH rises as air cools).

I think the clue is in your comment – “The kitchen has not been in use”. This means that the kitchen is probably on the cool side. Thus the RH will be high anyay and it wont take much of a drop for 100% to be reached – such as at the seals….

If you are renovating th ekicthen make sure you have good extraction intalled 🙂

I am selling my house built in the 1920’s to some jittery first time buyers. They are about to have a survey done (homebuyers report) in the next few days. I bought a meter with the sharp prongs from Amazon (a German make) which has been reporting a % of around 20-25% in an outside kitchen wall, the plaster is a little soft (was re-plastered in March) in places and the wall is always cold to the touch. The reading from the skirting is 5-6%.

Is this likely to be a significant issue on the survey? I don’t mind dropping the price but get the feeling our buyers will run faster than Mo Farah at the sound of “damp”!